[Qemu-devel] [PATCH 1/2] iothread: stash thread ID away

[Stefan Hajnoczi <stefanha@redhat.com>]

Keep the thread ID around so we can report it via QMP.

There's only one problem: qemu_get_thread_id() (gettid() wrapper on
Linux) must be called from the thread itself.  There is no way to get
the thread ID outside the thread.

This patch uses a condvar to wait for iothread_run() to populate the
thread_id inside the thread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 iothread.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/iothread.c b/iothread.c
index 033de7f..1a0d1ec 100644
--- a/iothread.c
+++ b/iothread.c
@@ -26,8 +26,15 @@ struct IOThread {
     QemuThread thread;
     AioContext *ctx;
     bool stopping;
+    int thread_id;
 };
 
+typedef struct {
+    QemuMutex init_done_lock;
+    QemuCond init_done_cond;    /* is thread initialization done? */
+    IOThread *iothread;
+} ThreadInitInfo;
+
 #define IOTHREAD_GET_CLASS(obj) \
    OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
 #define IOTHREAD_CLASS(klass) \
@@ -35,7 +42,15 @@ struct IOThread {
 
 static void *iothread_run(void *opaque)
 {
-    IOThread *iothread = opaque;
+    ThreadInitInfo *init_info = opaque;
+    IOThread *iothread = init_info->iothread;
+
+    iothread->thread_id = qemu_get_thread_id();
+
+    /* Signal that initialization is done */
+    qemu_mutex_lock(&init_info->init_done_lock);
+    qemu_cond_signal(&init_info->init_done_cond);
+    qemu_mutex_unlock(&init_info->init_done_lock);
 
     while (!iothread->stopping) {
         aio_context_acquire(iothread->ctx);
@@ -60,15 +75,30 @@ static void iothread_instance_finalize(Object *obj)
 static void iothread_complete(UserCreatable *obj, Error **errp)
 {
     IOThread *iothread = IOTHREAD(obj);
+    ThreadInitInfo init_info = {
+        .iothread = iothread,
+    };
 
     iothread->stopping = false;
     iothread->ctx = aio_context_new();
 
+    qemu_mutex_init(&init_info.init_done_lock);
+    qemu_cond_init(&init_info.init_done_cond);
+
     /* This assumes we are called from a thread with useful CPU affinity for us
      * to inherit.
      */
     qemu_thread_create(&iothread->thread, iothread_run,
-                       iothread, QEMU_THREAD_JOINABLE);
+                       &init_info, QEMU_THREAD_JOINABLE);
+
+    /* Wait for initialization to complete */
+    qemu_mutex_lock(&init_info.init_done_lock);
+    qemu_cond_wait(&init_info.init_done_cond,
+                   &init_info.init_done_lock);
+    qemu_mutex_unlock(&init_info.init_done_lock);
+
+    qemu_cond_destroy(&init_info.init_done_cond);
+    qemu_mutex_destroy(&init_info.init_done_lock);
 }
 
 static void iothread_class_init(ObjectClass *klass, void *class_data)
-- 
1.8.5.3